This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Application No. 2001-380371 filed Dec. 13, 2001.
1. Field of the Invention
The present invention relates to an electromagnetic valve device that supports a moving member in a reciprocating fashion and a manufacturing method thereof.
2. Description of the Related Art
At least one known electromagnetic valve device comprises a valve member reciprocating together with a moving member inside an electromagnetic driving portion. This controls the flow rate of a fluid that passes through a fluid path. In this electromagnetic valve device, the flow rate of the fluid is controlled by movement of the valve member so that the fluid path is opened or closed, or alternatively, the area of the fluid path is changed.
The moving member that drives the valve member is movably supported in a reciprocating manner in a stator. The conventional moving member is supported, for example, by a roller bearing. In recent years, there has been a demand for an electromagnetic valve device that can carry out various types of performance and yet still be manufactured at a minimal cost. This creates demand for a more inexpensive manner of supporting the moving member that does away with use of expensive roller bearing supports. A technique of directly supporting a moving member using a cup-shaped, non-magnetic member has been suggested. In this method, the non-magnetic member is located between the moving member and the stator, and the moving member moves slidably within the non-magnetic member.
In the above-mentioned device, where the moving member is supported by the non-magnetic member, the moving member and the non-magnetic member both slide against each other and thus the surfaces thereof are prone to wear. During operation of the electromagnetic valve device, the moving member always receives force in the reciprocating direction during movement. As a result, surface wear occurs between the outer wall of the moving member and the inner wall of the non-magnetic member that slide against each other. Typically, the moving member and the non-magnetic member are made of materials having a different hardness, and the member made of the material with the lower hardness wears faster. For example, when pure iron is used for the material of the moving member and stainless steel is used for the material of the non-magnetic member, the moving member whose hardness is lower wears faster. As a further example, when the moving member is coated with resin on the surface, the hardness of the surface of the moving member cannot be increased, and hence wear can hardly be reduced.
In the electromagnetic driving portion, the moving member and the stator form a magnetic circuit. Therefore, when the moving member is worn, the characteristics of the magnetic circuit, and more particularly, the operational characteristics of the electromagnetic driving portion will be changed. A further problem caused by wear is that the non-magnetic member provided between the moving member and the stator is thin. Therefore, when the non-magnetic member is worn, fluid from the fluid path can leak. A further problem of wear is that when the non-magnetic member is worn, the inner wall of the nonmagnetic member that slides against the outer wall of the moving member can become rough. This can result in operational failure and an increase in operation hysteresis. This in turn can cause the responsiveness of the device to deteriorate.
It is an object of the present invention to provide an electromagnetic valve device with high responsiveness that reduces wear of a moving member and a non-magnetic member sliding against the moving member and prevents contamination from entering the sliding part.
Another object of the invention is to provide a method of manufacturing an electromagnetic valve device that allows the hysteresis between the moving member and the non-magnetic member to be reduced.
In an electromagnetic valve device according to a first (or eighth) aspect of the present invention, the moving member has a hard portion at the sliding part that slides against the non-magnetic member. The hard portion has a hardness near that of a hardness of the non-magnetic member, and therefore, the outer wall of the moving member and the inner wall of the non-magnetic member that slide against each other have nearly the same hardness. Therefore, the wear of only one of the moving member and the non-magnetic member can be reduced. The hard portion has a hardness close to the non-magnetic member, so that the hardness of both the moving member and the non-magnetic member can be improved, and the wear caused by sliding can be reduced.
In the electromagnetic valve device according to a second aspect of the invention, the hard portion includes a metal layer containing a solid lubricating material. The solid lubricating material is a solid having a small friction coefficient, and the material lubricates the area between the surface of the hard portion and the inner wall of the non-magnetic member. Therefore, not only can the wear of the moving member and the non-magnetic member be reduced by the improvement in hardness, but also the sliding resistance between the moving member and the non-magnetic member can be reduced. By reducing the sliding resistance, the wear of the moving member and the non-magnetic member can be reduced. Since the sliding resistance is reduced, the driving force necessary to drive the moving member can be reduced. Furthermore, since the sliding resistance is reduced, the moving member can more smoothly move, which can improve the responsiveness and performance of the device.
In the electromagnetic valve device according to a third aspect of the invention, the solid lubricating material is in the form of particles made of fluororesin. Fluororesin has a small friction coefficient and is inexpensive, and hence the sliding resistance between the moving member and the non-magnetic member can be reduced without increasing the cost.
In the electromagnetic valve device according to a fourth aspect of the invention, the particles made of fluororesin are contained in the hard portion in the range from 5 vol % to 40 vol %. More specifically, the hard portion contains particles made of fluororesin in the described ratio. When the content of the particles made of fluororesin is smaller than 5 vol %, the wear of the moving member is not reduced, and hence the effect of mixing the particles made of fluororesin is not obtained. Meanwhile, when the content of the particles made of fluororesin is larger than 40 vol %, a sufficient hard portion is not formed, and hence the effect of reducing the wear by forming the hard portion is not provided. Therefore, by specifying the content of particles made of fluororesin to be in the above percentage range, wear and sliding resistance can be reduced.
In the electromagnetic valve device according to a fifth aspect of the invention, polytetrafluoroethylene may be applied as the fluororesin.
In the electromagnetic valve device according to a sixth aspect of the invention, molybdenum disulfide may be applied as the solid lubricating material.
In the electromagnetic valve device according to a seventh aspect of the invention, the metal forming the metal layer is nickel. Nickel has high hardness which is close to the hardness of stainless steel, for example, forming the non-magnetic member. Therefore, wear of the moving member and the non-magnetic member can be reduced.
In the electromagnetic valve device according to a ninth aspect of the invention, the moving member is formed to have an axial length larger than the axial length of the bottom-closed tube portion of the non-magnetic member. When the movement of the moving member in one direction is at its maximum, in other words, when the moving member is not attracted toward the suction portion, the end of the moving member on the side of the valve member is positioned closer to the side of the valve member than to the joint between the tube portion and the tapered portion. The moving member is protruded toward the inner circumferential side of the tapered portion from the bottom-closed tube portion. The moving member thus has a region that does not slide against the non-magnetic member. Therefore, contamination can be prevented from entering the inner circumferential side of the bottom-closed tube portion and between the moving member and the non-magnetic member that form the sliding part. Therefore, wear caused by contamination entering into the sliding part can be prevented.
In the electromagnetic valve device according to a tenth aspect of the invention, there is a gap formed between the outer wall of the suction portion and the inner wall of the large diameter portion. Along with the movement of the moving member, the fluid on the inner circumferential side of the stator is moved in the moving direction of the moving member. At that time, the fluid flows along the outer wall of the suction portion. Therefore, contamination contained in the fluid is allowed to travel with the flow of the fluid into the gap formed between the outer wall of the suction portion and the inner wall of the large diameter portion. The suction portion has its outer diameter expanded from the moving member side to the valve member in a tapered shape, and therefore the gap is narrower toward the valve member side. As a result, contamination is carried along with the flow of the fluid toward the valve member side of the gap and captured. In this way, contamination can be prevented from coming into the sliding part formed between the moving member and the non-magnetic member. Therefore, wear of the moving member and the non-magnetic member caused by the contamination can be reduced.
In the electromagnetic valve device according to an eleventh aspect of the invention, the hard portion containing a solid lubricating material is formed on the surface of the moving member, and then the surface of the hard portion is ground. When the hard portion is formed by electroless plating, the surface of the hard portion becomes rough by a hydrogen gas generated in the process of plating. Therefore, the hard portion is ground to smooth the surface. In this way, when the moving member having the hard portion is assembled in the inner circumference of the non-magnetic member, the sliding resistance between the moving member and the non-magnetic member is reduced. Consequently, hysteresis between the moving member and the non-magnetic member can be reduced.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.